One knows that when an automotive vehicle is driven on a roadway along a particular path of travel during the night, it is desirable to light the roadway in front of the vehicle in the best possible way over a sufficient distance to assure safety but limited by the power of the headlights. However, the intensity of the headlights should be as reduced as possible for the benefit of drivers of approaching or crossing vehicles. For this purpose, it is desirable, during movement of the vehicle, to maintain essentially constant a distance L between the vehicle and the point of impingement of the axis of the headlight beam on the road, along the assumed travel path along the road by rotation of the headlight around an axis essentially perpendicular to the path of travel of the vehicle and parallel to the road surface. One can of course satisfactorily adjust the vehicle headlights when the vehicle is empty, but this adjustment is destroyed or lost when the vehicle is loaded more or less in the front or in the rear, such variations in load taking place during acceleration or deceleration and appearing as a variation of the position or height of the center of gravity in relation to the roadway, hereafter called depth variations, and/or by a variation of the inclination of the vehicle in relation to the roadway, hereafter called attitude variation.
One has already proposed, for example in French Pat. No. 69-37513, a regulating apparatus for correcting the variation of inclination of the vehicle, that is to say variations in attitude of the vehicle. To do this, it has been proposed to adjust the position of the vehicle body in relation to the ground by means of sensors placed adjacent to the axles at the front and rear of the vehicle. If one calls d.sub.1 the distance of the body from the ground plumb with a point P.sub.1 near the front sensor, and d.sub.2 the distance of the body to the ground plumb with a point P.sub.2 near the rear sensor, and if one calls .alpha. an angle of adjustment of the position of the headlight beam axis in relation to the vehicle, the prior technique consists of adjusting the beam in such a way that the angle .alpha. would have a value .alpha.=K(d.sub.2 -d.sub.1)+K' a formula in which K and K' are constants.
Such adjustment takes into consideration variations in inclination of the vehicle but does not consider variations in depth or height. It has been ascertained that the adjustment thus obtained was insufficient and that it was then desirable to improve the characteristics of the adjustment. The object of this invention is an adjustment process considerably improving the maintaining of the distance L contant. To do this, according to the invention, one takes into consideration, to calculate the adjustment angle of the headlight beam, not only the inclination of the vehicle but also the height of the vehicle with respect to the road surface. This distance can be determined by a variable quantity (d.sub.1 +d.sub.2)/2 in such a way that the above mentioned angle .alpha. is defined by: .alpha.=K(d.sub.2 -d.sub.1)+K'+K"(d.sub.2 +d.sub.1), (d.sub.2 +d.sub.1).
K" being a constant.
According to the invention, an adjustment technique is used, in which the adjustment angle .alpha. of the headlight beam is caused by any appropriate means to stay essentially equal to a correction angle .alpha..sub.o defined by a formula in the form: EQU .alpha..sub.o =K.sub.1 (d.sub.1 -d.sub.2)+K.sub.2 d.sub.1 +K.sub.3
One has determined, surprisingly and unexpectedly, that almost exact constancy or stability can be obtained in the distance L when the coefficients K.sub.1 and K.sub.2, above defined, satisfy the relation: EQU l.sub.2 K.sub.1 +l.sub.1 K.sub.2 .perspectiveto.1
l.sub.2 designating the distance between the points P.sub.1 and P.sub.2 associated with the front axle and the rear axle, and l.sub.1 designating the distance between the point P.sub.1 and the axis of rotation, of the headlight to be adjusted. The precise adjustment which is obtained when one uses this technique, provides in all conditions of use of the vehicle, distance L constant within nearly 2% the distance L being in general, close to about 75 meters.
The present invention has correspondingly, as an object, a new adjustment procedure for the position of a headlight of an automotive vehicle in relation to the vehicle body, the headlight being capable of pivoting around an axis essentially parallel to the roadway and perpendicular to the vehicle travel path, and having as its position an angle .alpha., this procedure comprising using at least one sensor C.sub.1 near the front wheels and at least one sensor C.sub.2 near the rear wheels, the sensors C.sub.1 and C.sub.2 defining respectively the distance d.sub.1 and d.sub.2 corresponding to the distance of the body from the roadway plumb to the points P.sub.1 and P.sub.2 of the body, the point P.sub.1 being at a distance l.sub.1 from the axis of rotation of the headlight, and at a distance l.sub.2 from the point P.sub.2, the distances l.sub.1 and l.sub.2 being measured by projection on the line P.sub.1 P.sub.2, in which one defines an angle of correction .alpha..sub.o as a function of d.sub.1 and of d.sub.2 and in which one maintains the angle .alpha. equal to or near .alpha..sub.o, characterized by the fact that the angle .alpha..sub.o has as its value: EQU .alpha..sub.o =K.sub.1 (d.sub.2 -d.sub.1)+K.sub.2 d.sub.1 +K.sub.3
a formula in which K.sub.1, K.sub.2 and K.sub.3 are constants, K.sub.1 and K.sub.2 being related by the relationship K.sub.1 l.sub.2 +K.sub.2 l.sub.1 .perspectiveto.1.
It has been ascertained that the adjustment process according to the invention will permit obtaining more satisfactory results because the relation linking the values l.sub.1 and l.sub.2 and the constants K.sub.1 and K.sub.2 is better satisfied. In practice, one operates in such a way that the constants K.sub.1 and K.sub.2 are such that the expression K.sub.1 l.sub.2 +K.sub.2 l.sub.1 has a value in the range between 0.9 and 1.1. Of course, in the relation between the values of K.sub.1 and K.sub.2, the lengths l.sub.1 and l.sub.2 are expressed in the same units.
According to the invention, maintaining the value of .alpha. at the value of .alpha..sub.o, by adjustment of the headlights, can be done by an appropriate means, that is to say, either by a manually adjustable apparatus, or by an apparatus which automatic controls the adjustment. In the case of a manual adjustment, the user can for example place in coincidence a first indicator whose position is a function of .alpha. and a second indicator whose position is a function of .alpha..sub.o, this second indicator being controlled automatically from information provided by the sensors C.sub.1 and C.sub.2. In the case of an automatic adjustment, the angle .alpha. can be kept equal to .alpha..sub.o by an appropriate mechanical, hydraulic, electrical or other apparatus.
The present invention has also as an object an apparatus for performing the above described process.
In particular, the invention has as an object an apparatus with automatic adjustment for the orientation of a headlight of an automotive vehicle, this apparatus comprising near the front wheels of the vehicle at least one sensor C.sub.1 and near the rear wheels of the vehicle at least one sensor C.sub.2, the headlight being able to pivot around an axis essentially parallel to the roadway and transverse to the axis of the vehicle and being referenced in relation to the vehicle body by an angle .alpha., this apparatus comprising a calculator which, from the information d.sub.1 and d.sub.2 provided by the sensors C.sub.1 and C.sub.2 respectively, provides a voltage V.sub.1 (.alpha..sub.o), indicative of .alpha..sub.o, a datum information device providing a voltage V(.alpha.) indicative of .alpha., the angle of the headlight, V(.alpha.) being equal to V.sub.1 (.alpha..sub.o) when .alpha. equal .alpha..sub.o, the apparatus comprising in addition, a control means acting as a function of the difference V(.alpha.)-V.sub.1 (.alpha..sub.o), in the desired position of the headlight to cancel the difference, characterized by the fact that the calculator means generates the voltage V.sub.1 (.alpha..sub.o) by taking for .alpha..sub.o, the value .alpha..sub.o =K.sub.1 (d.sub.2 -d.sub.1)+K.sub.2 d.sub.1 +K.sub.3 with l.sub.2 K.sub.1 +l.sub.1 K.sub.2 .perspectiveto.1
In the definition given above, of the apparatus according to the invention, the symbols K.sub.1, K.sub.2, K.sub.3, l.sub.1, l.sub.2, d.sub.1, d.sub.2 have the significance already indicated. In a preferred embodiment the calculator means takes the form of an electronic circuit receiving from sensors C.sub.1 and C.sub.2, voltages as a function of d.sub.1 and d.sub.2 ; the voltages sent to the calculator by the sensors C.sub.1 and C.sub.2 are proportional to distances d.sub.1 and d.sub.2 ; the aforementioned information device being a potentiometer moved by an element joined to the headlight; the voltages V(.alpha.) and V.sub.1 (.alpha..sub.o) being sent by a subtractor unit whose output feeds, by means of an intermediate amplifier, the control means; the control means being an electric motor causing the headlight to pivot about it axis of rotation.
As is evident this apparatus can be made to have a limited zone or region of operation. More specifically, the angle .alpha. can be maintained between two limits, by providing a stop or blocking device to stop the motor or other control means when the voltage V(.alpha.) goes beyond either of the two limits between which it is desired to control the headlight beam. In this instance the apparatus of the invention comprises stop means associated with the information data means, the stop means receiving a voltage as a function of .alpha., comparing the voltage to predetermined limiting voltages, and stopping or blocking the control means when the information voltage exceeds the limiting voltages.
It is clear that the adjusting apparatus can be used to simultaneously adjust both headlights of a vehicle. However, a control or feedback loop can be provided for each headlight to permit individual control of the headlight at each side of the vehicle. Such apparatus advantageously comprises a single calculator which sends the same V.sub.1 voltage to each of two separate identical regulating loops, one controlling the position of each headlight.
This invention has as another object, a new commercial apparatus which constitutes an automotive vehicle comprising a means for pivoting the front headlights of a vehicle about an axis parallel to the road surface and perpendicular to the vehicle axis, characterized by the fact that the headlight is controlled by an apparatus to adjust its position, in the manner specified above.
For a better understanding of the invention there is now described a preferred embodiment, purely by way of example and not to be deemed limiting, in context with the drawings.